My suggestion is that you didn't know what you didn't know. Your Boss's boss should not have ambushed you like that either. Consider talking with your boss to have them expressly describe what their expectations are and how they are measuring them. Then, using the same way they are measuring, measure yourself and check with your boss to see if it matches up. It will help you understand what is expected and it will help them see how you hear what they are asking.
Also, have your boss put their expectations and their measurement criteria in an email to you, also email them with what you think the measurement should be and get them to confirm, in email that you are correct. With that information in hand, you cannot be ambushed like you were because you have "the receipts" as they say. What's more, if they fire your boss, and the next boss doesn't know what to put in your review, go over your email with them and that will set them straight.
My suggestion is that you didn't know what you didn't know. Your Boss's boss should not have ambushed you like that either. Consider talking with your boss to have them expressly describe what their expectations are and how they are measuring them. Then, using the same way they are measuring, measure yourself and check with your boss to see if it matches up. It will help you understand what is expected and it will help them see how you hear what they are asking.
Also, have your boss put their expectations and their measurement criteria in an email to you, also email them with what you think the measurement should be and get them to confirm, in email that you are correct. With that information in hand, you cannot be ambushed like you were because you have "the receipts" as they say. What's more, if they fire your boss, and the next boss doesn't know what to put in your review, go over your email with them and that will set them straight.